1 Field of the Invention
The present invention relates to a color cathode-ray tube, and more particularly, to a wire structure in which a natural frequency of a wire itself and a vibration damping force are improved to prevent a vibration of a neck glass caused due to an electrostatic force between the neck glass and a dynamic voltage focusing electrode.
2. Description of the Background Art
Generally, as shown in FIG. 1, a color cathode-ray tube includes a bulb-shaped funnel 1, a panel 2 with a fluorescent material coated on the inner surface thereof and being attached on the front surface of the funnel, an electron gun 4 encapsulated in a neck glass 3 formed at a rear side of the funnel 1, a stem pin 15 installed at the rear side of the neck glass 3, for applying a power to the electron gun 4, and a deflection yoke 5 installed at an outer periphery of the front side of the electron gun 4, that is, at an outer periphery of the rear side of the funnel 1.
In the color cathode-ray tube having the above-described structure, when a power is applied through the stem pin 15 to the electron gun 4, an electron beam is focused and accelerated to be injected toward the panel 2. At this time, an injection position of the electron beam is adjusted by the deflection yoke 5 to emit the fluorescent material coated on the inner surface of the panel 2.
The construction of the electron gun 4 for generating electron beams will now be described in detail with reference to FIGS. 2 and 3.
The stem portion is fused with the neck glass and sealed so that it may receive a voltage from an external source as being inserted inside the neck glass 3 at the rear side of the funnel 1, and a plurality of terminals are installed at the stem portion to make a stem pin 15.
A heater 41 is disposed connected to the stem pin 15. A cathode 42 is positioned at the front side of the heater 41. A first grid electrode 43 is disposed forwardly at a distance from the cathode 42. A second grid electrode 44, a third grid electrode 45 and a fourth grid electrode 46 are sequentially installed spaced apart from the first grid electrode 43. A static voltage focusing electrode 47, a dynamic voltage focusing electrode 48 and an anode 49 are disposed forwardly spaced apart from the fourth grid electrode 46.
Lower portions of each electrode are fixed to a bead glass 9 so that each electrode can be maintained at certain intervals, and a shield tap 7 is positioned in the middle of the upper and the lower faces of the bead glass 9.
A shield cup 14 for shielding a leakage magnetic field is installed at the end of the front side of the anode 49, and a bulb space connector (BSC) 50 for supporting the electron gun is connected at the front side of the shield cup 14.
Generally, in order to improve an image quality of a color cathode-ray tube, a dynamic voltage current is applied to one of the focusing electrodes 47 and 48 of the electron gun 4 and a static voltage current is applied to the other, or a dynamic voltage current is applied to at least two grid electrodes.
Thus, in order for the dynamic voltage current to be applied to the focusing electrodes 47 and 48, a wire 8 is connected between the stem pin 15 and the dynamic voltage focusing electrode 48. As shown in FIG. 4, the wire 8 is made of one-strand metal of which a rear end portion or a central portion is bent to rest on the upper surface of the bead glass 9.
In the conventional electron gun, as the heater 41 is heated upon receipt of the static voltage current through the stem pin 15, electron beams are injected from the cathode 42. The electron beams are controlled by the first grid electrode 43 and accelerated by the second grid electrode 44.
After being controlled and accelerated, the electron beams are focused and accelerated by a potential difference between the dynamic voltage applied to the dynamic voltage focusing electrode 48 and the constant-voltage applied to the static voltage focusing electrode 47, which passes through a slot of a shadow mask so as to be color-sorted and land on the fluorescent material coated on the inner surface of the panel 2 to emit the fluorescent material.
However, in the conventional electron gun, due to the dynamic voltage applied to the dynamic voltage focusing electrode 48 intended initially to improve the image quality, a large amount of dynamic voltage is induced at each point outside the neck glass 3.
At this time, the voltage applied to the electrode is defined by the following equation [1].
V=VDC+VAC COS xcfx89txe2x80x83xe2x80x83[1]
wherein VDC indicates a static voltage applied to the cathode, the heater, the first, the second and the third grid electrodes or the like of the electron gun, VAC COS xcfx89t indicates a dynamic voltage applied to the dynamic voltage focusing electrode, xe2x80x98Vxe2x80x99 indicates a voltage applied to the electrode, xcfx89 indicates an angular frequency, and xe2x80x98txe2x80x99 indicates time.
Accordingly, an electrostatic force is generated between the neck glass and the dynamic voltage focusing electrode as obtained in the following equation [2].                                                                         F                ⁡                                  (                  t                  )                                            =                              xe2x80x83                            ⁢                                                                    (                                                                                            σ                          b                                                /                        2                                            ⁢                                              ϵ                        0                                                              )                                    ⁢                                      CV                                          D                      ⁢                                              xe2x80x83                                            ⁢                      C                                                                      +                                                      (                                          1                      /                      2                                        )                                    ⁢                                      (                                          dC                      /                      dZ                                        )                                    ⁢                                      {                                                                  V                                                  D                          ⁢                                                      xe2x80x83                                                    ⁢                          C                                                2                                            +                                                                        (                                                      1                            /                            2                                                    )                                                ⁢                                                  V                                                      A                            ⁢                                                          xe2x80x83                                                        ⁢                            C                                                    2                                                                                      }                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    (                                                                                            σ                          b                                                /                        2                                            ⁢                                              ϵ                        0                                                              )                                    ⁢                                      DV                                                                  AC                        ⁢                        COS                                            ⁢                                              xe2x80x83                                            ⁢                      ω                      ⁢                                              xe2x80x83                                            ⁢                      t                                                                      +                                                      (                                          dC                      /                      dZ                                        )                                    ⁢                                      V                                          D                      ⁢                                              xe2x80x83                                            ⁢                      C                                                        ⁢                                      V                                                                  AC                        ⁢                        COS                                            ⁢                                              xe2x80x83                                            ⁢                      ω                      ⁢                                              xe2x80x83                                            ⁢                      t                                                                      +                                                                                                        xe2x80x83                            ⁢                                                (                                      1                    /                    4                                    )                                ⁢                                  (                                      dC                    /                    dZ                                    )                                ⁢                                  V                                      A                    ⁢                                          xe2x80x83                                        ⁢                    C                    ⁢                                          xe2x80x83                                        ⁢                    COS                    ⁢                                          xe2x80x83                                        ⁢                    2                    ⁢                                          xe2x80x83                                        ⁢                    ω                    ⁢                                          xe2x80x83                                        ⁢                    t                                    2                                                                                        [        2        ]            
wherein F(t) indicates an electrostatic force, "sgr"b indicates a surface charge density, ∈0 indicates a dielectric constant in vacuum, and xe2x80x98Cxe2x80x99 indicates an electrostatic capacity between the neck glass and the focusing electrode to which a dynamic voltage is applied.
When such a force is at work, the force according to third, fourth and fifth items of the above equation (2), not the static voltage, shows changes of COS xcfx89t. When it is simplified, the electrostatic force can be expressed by the following equation [3].
F(t)=∈0xc2x7Sxc2x7(dV)2/(2D2)xe2x80x83xe2x80x83[3]
That is, dV indicates a potential difference between electrodes, xe2x80x98Dxe2x80x99 indicates a distance between the electrodes, xe2x80x98Sxe2x80x99 indicates a facing area between the electrodes.
The electrostatic force vibrates the dynamic voltage focusing electrode 48, and the vibration of the dynamic voltage focusing electrode 48 is transmitted along the wire 8 to the stem pin 15 connected to the wire 8, to vibrate the neck glass 8.
Meanwhile, even though the dynamic voltage focusing electrode 48 is not vibrated by the electrostatic force, the wire 8 is vibrated owing to the change of the static electricity generated between the neck glass 3 and the dynamic voltage focusing electrode 48. This vibration makes the neck glass 3 vibrate, causing increased noise.
In addition, the vibration transmitted from the dynamic voltage focusing electrode 48 or the vibration occurring in the wire 8 generates a resonance if it is identical to the natural frequency of the neck glass 3, causing a high frequency noise which degrades the sensitivity characteristics of the cathode-ray tube.
Therefore, an object of the present invention is to provide an electron gun for a color cathode-ray tube in which a wire structure and form connected to apply a current to a focusing electrode are changed to vary a natural frequency of a wire and a vibration is prevented from being transmitted to a neck glass by improving a vibration damping capability, thereby restraining occurrence of a high frequency noise.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an electron gun for a cathode-ray tube having a neck glass formed at a rear side of a funnel, a stem pin applying an external voltage to an electron gun, a cathode electrode generating electron beams, a plurality of grid electrodes installed spaced apart from the electrode at predetermined intervals and each focusing electrode receiving a static voltage or a dynamic voltage, and an electron gun having an anode installed isolated from the focusing electrode, the electron gun being encapsulated in the neck glass, wherein a wire connecting the stem pin and the dynamic static voltage focusing electrode is formed to have a regular section change in a longitudinal direction, to thereby change a natural frequency.
For this purpose, several-strand wires are formed twisted together.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.